1. Field of the Invention
This invention relates generally to a method for assembling printed wiring board packages, and more specifically pertains to a method of attaching each electronic component to a substrate through an interface, to allow easy subsequent re-attachment of the electronic component without damage.
2. Description of the Related Prior Art
High density Printed Wiring Board (PWB) packages are composed of large area electronic components, such as Surface Mount Component (SMC) modules and Multichip Module (MCM) packages. In many civilian and military applications, such as space projects, the PWB packages have to withstand violent shaking which requires that all electronic components be firmly attached to the PWB substrate of the PWB package to prevent vibration-induced damages and dampen vibrations of the electronic components.
The conventional process for attaching electronic components, such as MCM packages, onto printed wiring boards includes a step of bonding the electronic component onto the printed wiring board substrate directly, without any intermediary, performed either prior to or after the soldering of the electronic component leads to the PWB. The bonding material is typically an epoxy adhesive, such as PR 4-34-1, which has a relatively good vibration damping and thermal conduction. FIG. 1 illustrates a greatly enlarged cross-sectional view of a result of the conventional adhesive bonding. It shows a printed wiring board substrate 10 and an electronic component 12, directly attached to the printed wiring board substrate 10 with an adhesive 14, having its electrical leads 16 soldered onto the printed wiring board substrate 10.
Although sufficient for small electronic components, the conventional bonding method can be difficult for attachment of large area MCMs. Moreover, quite often an electronic component has to be replaced or re-attached, either due to the electronic component malfunction or its redesign, and the bond has to be reworked. With the conventional process it is usually extremely hard or impossible to remove the electronic component from the PWB substrate without damage, unless the electronic component is very small and robust.
When the electronic component is large, and thus fragile, there is a considerable risk that the expensive electronic component will be damaged during rework. Once the adhesive is fully cured (solidified), it is extremely difficult to break the adhesive bond without damaging the electronic component, because an external heating machine, such as a heating gun, is used to heat and break the adhesive bond. However, due to its size, the machine heats the entire PWB package with all its electronic components and can easily cause the damage. The custom-made large area MCMs can be very expensive, and the cost of reworking these parts bears significant impact on product competitiveness.
Therefore, there is a need for an efficient process for fabrication of PWB packages, that includes an improved method for attaching and re-attaching large area electronic components onto printed wiring board substrates, at high production yield and without any degradation of their capabilities.